I have attached my edited rx-51 file for the US version. Make sure you backup your rx-51 file first before making any changes to it.

Also test the new settings using: Do this before rebooting since a small mistake in the rx-51 file will cause your n900 to hang endlessly at boot.

I added the following keyboard mappings:

Fn + Up = Page up
Fn + Down = Page down
Fn + Left = Home
Fn + Right = End
Fn + Backspace = Tab

Many small laptops have the "FN + arrow keys" mapped this way so I am already used to it.

Shaq